Lecture - 6 ( zeroth law of thermodynamics )

Before continuing in zeroth law, let us understand some basic terms -
  • Temperature is a parameter which represents average random energy per unit molecule. As random energy per unit molecules decreases then it means that temperature will get reduce and vice-versa.
  • Heat is the form of energy which transfers from it's high to low value. It is a method of energy transfer which takes place due to difference in temperature. As heat transfer from hot body to cold body, then random energy per unit molecule start decreasing in hot body which means that temperature start decreasing in hot body and random Energy per unit molecule start increasing in cold body which means that temperature of cold body start increasing gradually. All this process occurs because of heat transfer. 
  • Hotness or coldness is the feeling associated with heat transfer rate.
This basic concept is important to understand, so now let's move zeroth law.

Zeroth law of thermodynamics

Zeroth law of thermodynamics was given by Fowler in 1931. According to zeroth law of thermodynamics If body A and B are separately in thermal equilibrium with body C then they are also in thermal equilibrium with each other.
In zeroth law body C acts as thermometer and the zeroth law is used for temperature measurement.
consider the figure below in which body A and body C are in thermal equilibrium and body B and body C are in thermal Equilibrium.

Zeroth law of thermodynamics use behind measurement of temperature. Let's understand this with the help of practical example. Whenever we measure the temperature of our body from thermometer then zeroth law of thermodynamics is used behind it but most of us are not aware. If we relate this with our definition of zeroth law then body A is Mercury present in thermometer, body C is glass of thermometer and body B is human body.

For video lecture check this out Mechanical education hub 

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